Official C12 Clone - Build and Support Thread
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Matador
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R9 and R10 don't impact the DC voltage on B+: C1 and C2 don't either. So changing R6 to 499K reduces the bleed current which means less drop through R1+R2+R3.
So if you swap this same tube back into the first working mike, does it trim out to 120V properly? If you use this second mike on the first mike's power supply, does it behave the same? Are both PSU's trimmed to the same bias voltage (around -1V) after the tubes warm up?
So if you swap this same tube back into the first working mike, does it trim out to 120V properly? If you use this second mike on the first mike's power supply, does it behave the same? Are both PSU's trimmed to the same bias voltage (around -1V) after the tubes warm up?
Melodeath00
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Can we talk about the PSU a bit? I remember awhile back there was a discussion of C4 in the PSU having a 20% tolerance, and how that was the possible cause of sound differences between PSU.
What exactly does C4 do, and how does it affect the mic's sound? Does it change the impedance that the tube sees? Could we use this to our advantage to alter the tonal character of our mic?
Also, is it possible to modify the PSU to half-wave rectification, or would you basically have to begin from scratch?
What exactly does C4 do, and how does it affect the mic's sound? Does it change the impedance that the tube sees? Could we use this to our advantage to alter the tonal character of our mic?
Also, is it possible to modify the PSU to half-wave rectification, or would you basically have to begin from scratch?
Matador
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C4 is the last bypass/filter cap, and it's capacitance informs the cutoff frequency of the last filter section.
If you look at a transient load simulation, this cap provides the current to service the load since the output impedance of the supply is so high. It's debatable whether this would have an audible effect, since these kinds of transients contain frequencies well in excess of the audio range. But it might be worth experimenting!
Changing the design to half-wave is pretty simple, and doesn't require a new board:
1) Omit D1, D3, and D4
2) Wire a small jumper across where D3 would be placed (like you were shorting out the diode, which isn't there)
3) Reduce R1, R2, and R4 by roughly half
Reducing the power supply impedance (from step #3 above) would have a large impact on the sound however...
If you look at a transient load simulation, this cap provides the current to service the load since the output impedance of the supply is so high. It's debatable whether this would have an audible effect, since these kinds of transients contain frequencies well in excess of the audio range. But it might be worth experimenting!
Changing the design to half-wave is pretty simple, and doesn't require a new board:
1) Omit D1, D3, and D4
2) Wire a small jumper across where D3 would be placed (like you were shorting out the diode, which isn't there)
3) Reduce R1, R2, and R4 by roughly half
Reducing the power supply impedance (from step #3 above) would have a large impact on the sound however...
Melodeath00
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Matador said:
Thanks. Just a little bit over my head here... So C4 determines the cutoff frequency at the lows or the highs?
What sort of effect would step 3 have on the sound? Would it put the impedance further away from/lower than the original vintage design?
Matador
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Melodeath00 said:
It determines the effectiveness of the filter which is there to reduce 120Hz hum from the B+ line. Smaller C moves the filter up in frequency, making it (slightly) less effective at hum filtering.
Original PSU was half-wave, so lowering the series filter resistances makes it more in-line with the original values (which were a total of about 40K if memory serves).
vinylwall
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Chunger, How close are you getting to having the newest revision of the PCB in stock?
Matador
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vinylwall said:
Not Chunger's fault, it's mine: I've been slammed at work and haven't submitted Gerbers for him so he can make the new version.
It's in process: stay tuned.
Category 5
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Any chance you will add a spot to mount the transformer to? I hate the zip tie method and dislike floating around iron. 
chunger
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Category 5 said:Any chance you will add a spot to mount the transformer to? I hate the zip tie method and dislike floating around iron.
We do not have zip tie mounts for the transformer. I can see about getting some loose metal bell housings from Alctron if that method is preferred. The reason I do not want to make a longer board with a hole for the transformer is Cinemag is prototyping a large core transformer that will fit in the body, and I do not want to lock people into the small core options.
Category 5
Well-known member
chunger said:Category 5 said:Any chance you will add a spot to mount the transformer to? I hate the zip tie method and dislike floating around iron.
We do not have zip tie mounts for the transformer. I can see about getting some loose metal bell housings from Alctron if that method is preferred. The reason I do not want to make a longer board with a hole for the transformer is Cinemag is prototyping a large core transformer that will fit in the body, and I do not want to lock people into the small core options.
That would be great. It's my preferred method. (Bell housing)
vinylwall
Well-known member
kazanoom said:
Some might be tempted to help you here, but unfortunately the new PCB's aren't done yet. Matador has been very busy and hasn't had a chance to get Chunger what he needs. Believe me, I've been checking the Studio 939 store EVERY day to see if they are there. I'm ready to roll on this (my second C12 build)
))))))))))))))))
Matador
Well-known member
vinylwall said:kazanoom said:
Some might be tempted to help you here, but unfortunately the new PCB's aren't done yet. Matador has been very busy and hasn't had a chance to get Chunger what he needs. Believe me, I've been checking the Studio 939 store EVERY day to see if they are there. I'm ready to roll on this (my second C12 build)
Update: I submitted the panel order last week, and just received a shipment notification for the boards to Chunger. Stay tuned, the wait is almost over.
vinylwall
Well-known member
Matador said:vinylwall said:kazanoom said:
Some might be tempted to help you here, but unfortunately the new PCB's aren't done yet. Matador has been very busy and hasn't had a chance to get Chunger what he needs. Believe me, I've been checking the Studio 939 store EVERY day to see if they are there. I'm ready to roll on this (my second C12 build)
Update: I submitted the panel order last week, and just received a shipment notification for the boards to Chunger. Stay tuned, the wait is almost over.
I was able to place an order for the v1.4 boards!!! I know Chunger is busy (as I still have a couple orders before this one in his queue that have been placed weeks ago). While I wait, Matador, will there be any updates to the first page of this build thread to reflect any differences in the v1.4 board? Thanks.
Matador
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Yes, I can do that. I'll update the schematic bundle (largely unchanged expect for a few component values) and BOM.
vinylwall
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Matador said:
Hi Matador. Will you have a chance to update the docs for v1.4 soon? I'm ready to roll on this now
Matador
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vinylwall said:Matador said:
Hi Matador. Will you have a chance to update the docs for v1.4 soon? I'm ready to roll on this now
Argh - my password appears to have reset which is causing my upload to fail.
If you PM me your email address I'll email the PDF bundle while I fix the account problem on my web site.
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